Lane keep control for vehicle

Abstract

A vehicle includes a first actuating system having an automatic steering actuator to bring the front wheel steer angle to a calculated target front wheel steer angle for lane keeping, and a second actuating system such as a front and rear roll stiffness distribution control system, a front and rear driving force distribution control system, a rear wheel steering system, and a differential limiting force control system. By controlling the second actuating system in accordance with the automatic steering operation, a control unit adjusts the steering characteristic of the vehicle in a direction to improve the yawing response or in a direction to improve the running stability.

What is claimed is:  
     
       1. A lane keeping apparatus comprising: 
       an automatic steering section comprising a steering actuator to bring an actual wheel steer angle of a controlled vehicle to a target wheel steer angle calculated for lane keeping; and  
       a steering characteristic adjusting section to adjust a steering characteristic of the controlled vehicle, in the case of an automatic steering mode of the automatic steering section, in a first direction to improve a yawing response of the controlled vehicle or in a second direction to improve a running stability of the controlled vehicle in accordance with a steering amount of the automatic steering section,  
       wherein the steering characteristic adjusting section is configured to adjust the steering characteristic of the controlled vehicle in the case of the automatic steering mode of the automatic steering section, in the first direction to improve the yawing response of the controlled vehicle when the steering amount of the controlled vehicle is increased and in the second direction to improve the running stability of the controlled vehicle when the steering amount of the controlled vehicle is decreased.  
     
     
       2. The lane keeping apparatus as claimed in  claim 1 , wherein the automatic steering section is configured to control the actual wheel steer angle of the controlled vehicle in accordance with a yaw angle of the controlled vehicle with respect to a lane, a side deviation of the controlled vehicle in the lane, and a curvature of the lane ahead of the controlled vehicle. 
     
     
       3. The lane keeping apparatus as claimed in  claim 1 , wherein the steering characteristic adjusting section comprises at least one of a front and rear roll stiffness distribution control system arranged to vary a front and rear roll stiffness distribution, a front and rear driving force distribution control system arranged to vary front and rear driving force distributions, a four wheel steering system arranged to vary front and rear wheel steer angles, and a differential limiting amount control system arranged to vary a drive wheel differential limiting amount. 
     
     
       4. The lane keeping apparatus as claimed in  claim 3 , wherein the front and rear roll stiffness distribution control system of the steering characteristic adjusting section comprises an active suspension system which comprises hydraulic cylinders each of which is disposed between a vehicle body and one of front and rear wheels of the controlled vehicle, to vary a distance between the vehicle body and the wheel, and the steering characteristic adjusting section is configured to adjust the steering characteristic in the first direction to improve the yawing response of the controlled vehicle by increasing fluid pressures supplied to the hydraulic cylinders for the rear wheels over fluid pressures for the front wheels, and to adjust the steering characteristic in the second direction to improve the running stability of the controlled vehicle by increasing the fluid pressures to the hydraulic cylinders for the front wheels over the fluid pressures for the rear wheels. 
     
     
       5. The lane keeping apparatus as claimed in  claim 3 , wherein the front and rear driving force distribution control system of the steering characteristic adjusting section comprises an actuator to vary a front driving force distribution allotted to front wheels and a rear driving force distribution allotted to rear wheels of the controlled vehicle, and the steering characteristic adjusting section is configured to adjust the steering characteristic in the first direction to improve the yawing response of the controlled vehicle by increasing the rear driving force distribution, and to adjust the steering characteristic in the second direction to improve the running stability of the controlled vehicle by increasing the front driving force distribution. 
     
     
       6. The lane keeping apparatus as claimed in  claim 3 , wherein the four wheel steering system of the steering characteristic adjusting section is arranged to vary a primary wheel steering amount of primary steerable wheels ( 1 FL,  1 FR) of the controlled vehicle and a secondary wheel steering amount of secondary steerable wheels of the controlled vehicle, and the steering characteristic adjusting section is configured to adjust the steering characteristic in the first direction to improve the yawing response of the controlled vehicle by decreasing the secondary wheel steer amount in an in-phase direction, and to adjust the steering characteristic in the second direction to improve the running stability of the controlled vehicle by increasing the secondary wheel steering amount in the in-phase direction. 
     
     
       7. The lane keeping apparatus as claimed in  claim 3 , wherein the differential limiting amount control system of the steering characteristic adjusting section is arranged to vary a differential limiting amount of drive wheels of the controlled vehicle, and the steering characteristic adjusting section is configured to adjust the steering characteristic in the first direction to improve the yawing response by increasing the differential limiting amount, in the second direction to improve the running stability by decreasing the differential limiting amount in the case of cornering acceleration, and to adjust the steering characteristic in the first direction to improve the yawing response by decreasing the differential limiting amount, and in the second direction to improve the running stability by increasing the differential limiting amount in the case of cornering deceleration. 
     
     
       8. The lane keeping apparatus as claimed in  claim 3 , wherein the lane keeping apparatus further comprises a sensor to sense a degree of turning motion of the controlled vehicle; the steering characteristic adjusting section comprises first and second systems which are one and another of the front and rear roll stiffness distribution control system, the front and rear driving force distribution control system, the four wheel steering system and the differential limiting amount control system; and the steering characteristic adjusting section further comprises a control unit to adjust the steering characteristic by using a selected one of the first and second systems selected in accordance with the degree of turning motion. 
     
     
       9. The lane keeping apparatus as claimed in  claim 8 , wherein the first system is the roll stiffness distribution control system and the second system is the four wheel steering system, the sensor senses a lateral acceleration of the controlled vehicle as the degree of turning motion, and the control unit is configured to adjust the steering characteristic with the four wheel steering system when the lateral acceleration is in a smaller lateral acceleration region, and with the roll stiffness distribution control system when the lateral acceleration is in a larger lateral acceleration region larger than the smaller lateral acceleration region. 
     
     
       10. The lane keeping apparatus as claimed in  claim 8 , wherein the first system is the front and rear driving force distribution control system and the second system is the four wheel steering system, the sensor senses a lateral acceleration of the controlled vehicle as the degree of turning motion, and the control unit is configured to adjust the steering characteristic with the four wheel steering system when the lateral acceleration is in a smaller lateral acceleration region, and with the front and rear driving force distribution control system when the lateral acceleration is in a larger lateral acceleration region larger than the smaller lateral acceleration region. 
     
     
       11. The lane keeping apparatus as claimed in  claim 1 , wherein the lane keeping apparatus further comprises a sensor to sense a vehicle turning condition indicative of steepness of a turn of the controlled vehicle, and the steering characteristic adjusting section is configured to adjust the steering characteristic only when the vehicle turning condition is equal to or greater than a threshold. 
     
     
       12. The lane keeping apparatus as claimed in  claim 1 , wherein the lane keeping apparatus further comprises a vehicle behavior sensor to sense a vehicle behavior of the controlled vehicle, and the steering characteristic adjusting section is configured to detect a predetermined condition having a tendency to lower the running stability of the controlled vehicle in accordance with the vehicle behavior and to refrain from adjusting the steering characteristic in the first direction to improve the yawing response when the predetermined condition is detected. 
     
     
       13. The lane keeping apparatus as claimed in  claim 1 , wherein the lane keeping apparatus further comprises a sensor for determining a vehicle speed of the controlled vehicle, and the steering characteristic adjusting section is configured to adjust the steering characteristic in the direction to improve the running stability of the controlled vehicle as the vehicle speed increases. 
     
     
       14. The lane keeping apparatus as claimed in  claim 1 , wherein the steering actuator of the automatic steering section is configured to steer front wheels of the controlled vehicle to reduce a deviation of the actual wheel steer angle, which is an actual front wheel steer angle of the controlled vehicle, from the target wheel steer angle, which is a target front wheel steer angle calculated for lane keeping; and wherein the steering characteristic adjusting section is configured to determine a modification quantity in accordance with the target front wheel steer angle, and to adjust the steering characteristic of the controlled vehicle in accordance with the modification quantity in the case of the automatic steering mode of the automatic steering section. 
     
     
       15. The lane keeping apparatus as claimed in  claim 14 , wherein the steering characteristic adjusting section comprises a control unit to increase the modification quantity with increase in the target front wheel steer angle. 
     
     
       16. The lane keeping apparatus as claimed in  claim 15 , wherein the control unit determines the modification quantity which is a product obtained by multiplying the target front wheel steer angle by a control gain; and wherein the lane keeping apparatus further comprises a sensor to determine a vehicle speed of the controlled vehicle, and the control unit is configured to determine the control gain in accordance with the vehicle speed so that the control gain is decreased as the vehicle speed increases. 
     
     
       17. The lane keeping apparatus as claimed in  claim 1 , wherein the steering characteristic adjusting section comprises a vehicle control system arranged to vary a manipulated variable affecting the steering characteristic of the vehicle, and a control unit to adjust the steering characteristic of the vehicle by modifying the manipulated variable in accordance with the steering amount of the automatic steering section. 
     
     
       18. A lane keeping apparatus comprising: 
       automatic steering means for calculating a target wheel steer angle for lane keeping and for varying a first manipulated variable to bring an actual wheel steer angle of a controlled vehicle to the target wheel steer angle; and  
       steering characteristic adjusting means for adjusting a steering characteristic of the controlled vehicle in the case of an automatic steering mode of the automatic steering means, by varying a second manipulated variable affecting the steering characteristic of the vehicle, in accordance with a parameter representing a steering amount of the automatic steering means in one of a first direction to improve a yawing response of the controlled vehicle and a second direction to improve a running stability of the controlled vehicle in dependence on the steering amount, the second manipulated variable being a manipulated variable distinct from the first manipulated variable.  
     
     
       19. The lane keeping apparatus as claimed in  claim 18 , wherein in the case of the automatic steering mode, the steering characteristic adjusting means includes means for adjusting the steering characteristic of the controlled vehicle in the first direction to improve the yawing response of the controlled vehicle when the steering amount of the controlled vehicle is increased and in the second direction to improve the running stability of the controlled vehicle when the steering amount of the controlled vehicle is decreased. 
     
     
       20. A lane keep control method comprising: 
       calculating a target wheel steer angle to achieve an automatic steering control for lane keeping;  
       determining a modification quantity to adjust a steering characteristic of the controlled vehicle in accordance with a parameter representing a steering amount of the automatic steering control; and  
       controlling an actual wheel steer angle of the controlled vehicle by varying a first manipulated variable so as to bring the actual wheel steer angle to the target wheel steer angle, and adjusting the steering characteristic of the controlled vehicle, by modifying a second manipulated variable affecting the steering characteristic of the vehicle, in accordance with the modification quantity in one of a first direction to improve a yawing response of the controlled vehicle and a second direction to improve a running stability of the controlled vehicle.  
     
     
       21. The method as claimed in  claim 20 , wherein the steering characteristic of the controlled vehicle is adjusted in the first direction to improve the yawing response of the controlled vehicle when the steering amount of the controlled vehicle is increased, and in the second direction to improve the running stability of the controlled vehicle when the steering amount of the controlled vehicle is decreased. 
     
     
       22. A vehicle comprising: 
       a first actuating system comprising a lane keeping automatic steering actuator to vary a first manipulated variable to bring an actual wheel steer angle of the vehicle to a target wheel steer angle calculated for lane keeping;  
       a second actuating system to vary a second manipulated variable affecting a steering characteristic of the vehicle; and  
       a control unit to adjust the steering characteristic of the vehicle by modifying the second manipulated variable in accordance with a steering amount of the first actuating system.  
     
     
       23. The vehicle as claimed in  claim 22 , wherein the control unit is configured to adjust the steering characteristic of the controlled vehicle in a first direction to improve the yawing response of the controlled vehicle when the steering amount of the controlled vehicle is increased and in a second direction to improve the running stability of the controlled vehicle when the steering amount of the controlled vehicle is decreased.